Parts for your 2018 Mazda 3-Oxygen sensor

2018 Mazda 3 Oxygen Sensor — What It Does and When to Replace It

Yes, the 2018 Mazda 3 is fitted with oxygen sensors. Technical sources that confirm this include the Mazda 3 (BM/BN) workshop manual for the Skyactiv-G engines (PE-VPS 2.0L and PY-VPS 2.5L) and Mazda’s electronic parts catalog, both of which list a front air–fuel ratio (A/F) sensor in the exhaust manifold and a rear heated oxygen sensor (HO2S) after the catalytic converter. Modern OBD-II/ADR-compliant engine management (ADR 79/04, UNECE R83 aligned) also requires upstream and downstream sensors for closed-loop fuelling and catalyst monitoring, which the 2018 Mazda 3 supports.

On this model, the front wideband A/F sensor continuously measures oxygen content so the ECU can fine-tune fuel trims for smooth running, good power, lower emissions, and better fuel economy. The rear sensor mainly checks how well the catalytic converter is doing its job. If either sensor goes lazy or fails, the ECU may swing to a richer mix, fuel use goes up, and the check engine light is likely to appear with codes such as P0131/P0132, P0138, P2195/P2196, or catalyst efficiency codes.

There’s no fixed service interval for oxygen sensors on the 2018 Mazda 3, but they’re wear items. Many last beyond 160,000 km, though lots of short trips, oil consumption, or exhaust leaks can shorten their life. Signs it’s time to act include poorer fuel economy, rough idle, a sulphur smell from the exhaust, failed WOF/Roadworthy emissions checks, or stored OBD-II faults.

• Inspect for exhaust leaks before and after the cat—leaks can mimic sensor faults.
• Use live data to confirm a slow or stuck sensor (front A/F should respond quickly, rear should be stable with a healthy cat).
• When replacing, use the exact part number (Denso is OE on Mazda). Most new sensors arrive with the correct anti-seize on the threads—avoid adding extra unless specified.
• Fit to a cold exhaust, avoid twisting the harness, and torque to workshop specs (typical range ~30–45 N·m, check the Mazda manual for your engine).
• Clear codes and perform an idle/drive cycle so the ECU can relearn fuel trims.

Keeping the oxygen sensors healthy helps the Mazda 3 sip fewer litres per 100 km, keeps the cat safe, and makes the drive feel crisp and responsive.

How many oxygen sensors does a 2018 Mazda 3 have and where are they?

It has two. The front wideband air–fuel ratio sensor is mounted in the exhaust manifold (upstream), and the rear heated oxygen sensor sits after the catalytic converter (downstream) in the exhaust.

How often should the oxygen sensor be replaced?

There’s no set interval. Many last 160,000–200,000 km, but replacement should be based on symptoms or test results. If fuel economy drops, a check engine light appears, or scan data shows slow response, it’s time to test and likely replace.

Is it okay to keep driving with a bad oxygen sensor?

Short-term driving is usually possible, but it can burn more fuel and risk damaging the catalytic converter if left too long. Best to diagnose early and sort it before it becomes a bigger bill.